1. Field of the Invention
The present invention relates to an image display unit with an optical sensor incorporated in a display panel. In particular, the invention relates to an image display unit with screen input function, by which image data can be directly inputted to screen without decreasing numerical aperture of pixel.
2. Description of the Prior Art
An image display unit with screen input function is known, which inputs information by touching operation (hereinafter may be referred simply as “touch”) by touching the screen with a finger of a user. This type of image display unit is used in a portable terminal with a touching sensor such as PDA or in a stationary type client guiding terminal. As the image display unit screen input function, there are several types: a type to detect the change of resistance in the portion pressed by touching, a type to detect the change of capacity, or a type to detect the change of light amount in the portion shielded by touching.
In particular, efforts have been made in recent years, to develop a type of image display unit to detect coordinates of the touching portion by finding the changes of the light amount of the external light in the pixel structure on the screen. For instance, the Patent Document 1 discloses a light sensing element (optical sensor) by a thin-film transistor (TFT) for each pixel on a liquid crystal display panel, which makes up a liquid crystal display unit.
FIG. 20 shows an equivalent circuit diagram to explain pixel arrangement in a conventional example of a general type liquid crystal display panel with optical sensor for each pixel unit as disclosed in the Patent Document 1. This liquid crystal display panel comprises a plurality of gate lines (GLs), a plurality of data lines (DLs), a first switching element (Q1) electrically connected to each of the gate lines (GLs) and the data lines (DLs), and a liquid crystal capacitor (CLC) and a first storage capacitor (CST1) each connected to the first switching element (Q1), Further, it comprises a first voltage line (VL1), a second voltage line (VL2), a second switching element (TS1) to detect the intensity of external light and to convert it to electric current, a second storage capacitor (CST2) for preserving electric charge generated by electric current provided from the second switching element (TS1), a third switching element (TS2) to output the electric charge maintained at the second storage capacitor (CST2), and a reading line (ROL). The second switching element (TS1), the second storage capacitor (CST2), and the third switching element (TS2) make up together a type of optical sensor.    [Patent Document 1] JP-A-2005-129948.